Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

475
FXUS63 KLOT 262343
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
Issued by National Weather Service Milwaukee/Sullivan WI
643 PM CDT Thu Mar 26 2026

.KEY MESSAGES...

- A powerful cold front is rolling southward through the area
  today with a notable temperature drop behind it.

- Thunderstorms are likely to develop near the front this
  afternoon, with the highest chances of thunderstorms near and
  south of I-80. There is a level 3 out of 5 severe threat in
  the region with large, possibly destructive hail and damaging
  winds the main threats.

- Conditions will turn much colder Friday before a warming
  trend develops over the weekend.

&&

.DISCUSSION...
Issued at 1227 PM CDT Thu Mar 26 2026

Today and tonight...

A sharp cold front, enhanced by the cold waters over the lake,
is rolling swiftly southward across northern Illinois early
this afternoon. By about 2 PM, this will be in the vicinity of a
Rochelle to Joliet to Valparaiso line, and by 4-5 PM near a
Pontiac to Rensselaer line before finally getting shoved south
of the entire forecast area through 6-7 PM. For the locales
south of I-80, the hourly temperature drop as the front passes
may be near 20+ degrees as the front will be arriving during
peak heating.

A series of diffuse mid-level waves, coincident with with enhanced
moisture above 14 kft and steep 500-400 mb lapse rates will
continue to support a threat for isolated to widely scattered
high-based showers and storms through mid afternoon prior to the
"main show". Overall, the severe threat with these is probably a
level 1 out of 5, with steep mid-level lapse rates supportive of
some marginally severe hail.

Through about 4 PM, a modest 700 mb shortwave that`s currently
pushing east across Iowa will shift across northern Illinois.
This will likely be the feature that finally helps lift/erode
lingering capping (both for surface based and elevated parcels),
leading to the development of initial robust thunderstorms
through 4 to 6 PM, both on the leading edge of the cold front
(which will be across our very far southern CWA) and atop the
front itself up through about I- 88. It remains a bit unclear
what the coverage of elevated convection will be during this
window, with recent hires guidance backing off a bit. However,
given the look on forecast soundings and the ever-increasing
(albeit modest) large scale ascent, suspect we will see at least
widely scattered elevated convective cores developing through 6
PM. Coverage should then generally expand through the early
evening hours as additional moistening takes place above the
frontal inversion.

If a storm or two manage to fire well ahead of the cold front in
the 4 to 6 PM timeframe in the vicinity of US-24, there would
be a brief tornado threat, but this window will close rapidly as
the boundary surges southward. Large hail--perhaps with a few
instances of very large 2+" diameter hail--remain the main
threat, with an eventual transition to bowing segments/clusters
with an attendant localized damaging wind threat. Based on the
latest guidance, the severe threat in general has shifted about
20-30 miles south from yesterday, with the main MUCAPE reservoir
setting up near and south of I-80. The main overlap of the very
strongest ascent and most significant instability looks to
occur south of about I-80 and east of I-55, and this is where we
expect the severe threat to maximize into this evening.

Broad southwesterly 700 mb flow will continue to overtop the
front well into this evening which will likely lead to several
rounds of elevated convective development. After 9-10 PM, any
lingering severe threat should transition well south of I-80,
with the severe window ending completely by midnight-1 AM.

A localized training/heavy rainfall threat will exists through
this evening. Given the ongoing drought/dry conditions,
expectation is for any flood threat to remain isolated and thus
have refrained from issuing a flood watch at this time.


Friday and beyond...

Much colder conditions are expected in the wake of this system
tonight into Friday. Highs Friday should mainly top out in the
low-mid 40s, except holding in the 30s near the lake. A
shortwave trough embedded within the broader amplifying northern
stream trough is expected to dig southeastward into the western
Great Lakes Friday. Most guidance suggests air mass will be too
dry to support any precip, though there is some signal for
sufficient low-level moistening/0-3 km CAPE to support some
rain/snow shower activity Friday afternoon over far NE IL. These
models are likely too moist and opted to keep the forecast dry
for now, thinking that the better precip threat will remain
farther north across WI and MI.

After a cool start, Saturday looks like a nice day as the core
of the surface high crests overhead. Initially light and
variable winds will become south to southwesterly during the
afternoon as the high shifts off to our east. Conditions will be
quite dry with afternoon RH values likely dropping into the
20-30 percent range (if not lower than this). Depending on how
high we mix, could be a slightly elevated fire danger across our
westernmost locales during the afternoon.

The surface pressure gradient will tighten up a bit more on
Sunday as the next surface low gets going east of the
Continental Divide. A low-amplitude shortwave is forecast to
transit the region during the afternoon which may end up tossing
some increase mid and high-level cloud cover our way, possibly
tempering insolation some. If this cloud cover ends up remaining
more scattered in nature, temperatures will rise into the mid
to upper 60s, with afternoon RH values possibly falling near or
under 30 percent. With somewhat breezier southerly flow, there
may be a slightly increased fire danger on Sunday as a result.

During next week, medium range guidance generally suggests that
the dominant upper ridge that`s been in place this past week
will transition to broad longwave troughing. This in turn will
establish more of a west to southwesterly flow aloft regime
across the central CONUS which will support a period of above
average temperatures along with unsettled weather conditions at
times.

An initial area of low pressure is forecast to develop
northeastward into Iowa/Minnesota Monday night into Tuesday
which will drag a warm frontal zone northward through the
region. An associated mid-level wave accompanying this feature
will support a period of showers and thunderstorms in the
region, particularly Monday evening and overnight. While mid-
level shear will be modest to strong, a general dearth of
instability currently looks like it`ll limit the strong- severe
potential in the area. An associated cold front is slated to
shift through the forecast area Tuesday night into Wednesday
with additional shower chances.

Model spread increases during the Wednesday-Thursday timeframe,
with  solutions varying from cool and dry post-frontal/easterly
flow across the area, to the main baroclinic zone stalling
overhead with additional disturbances riding northeastward along
it.

Carlaw

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 631 PM CDT Thu Mar 26 2026

- Ongoing shower and embedded TS activity tapers off in a north to
  south manner later this evening.

- Strong and gusty northeasterly winds continue into tonight,
  decelerating into Friday morning. A north to northwest breeze
  builds into Friday afternoon.

- Roughly 1,000 ft Fuel-Alt MVFR ceilings expected to arrive as
  the rain showers continue this evening, with a brief window of
  IFR cigs too. Cigs lift closer to 1,500-2,000 ft later
  tonight, then lift/scatter to predominantly VFR for Fri
  afternoon.

Ongoing rain showers and embedded thunderstorms will continue over
the next few hours, gradually tapering off in a north to south
manner into tonight. The additional rainfall should be
accompanied by a decline in ceiling heights (likely to Fuel-Alt
MVFR, and even IFR levels for at least a brief period). Strong
north-northeasterly winds with gusts to around 30-35 knots
continue through the evening, with some crosswind issues for W-E
runways remaining possible. Winds will make a gradual decline
after midnight tonight through dawn Friday morning. Ceilings
gradually lift back to MVFR levels late tonight into Friday
morning.

Ceilings lift and scatter to predominantly VFR levels through
Friday, though the exact timing remains uncertain. Most guidance
suggests predominantly VFR by early Friday afternoon. The
northeasterly breeze continues into Friday morning, backing
north to northwesterly towards midday Friday. Areas east of I-57
might hang on to due north or northeasterly winds Friday
afternoon (roughly half of the available guidance reflects this
scenario, with the other half allowing northwest winds to spread
in).

Sheppard

&&

$$

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